text: In general it is more important to cover more fields of the tech by the techteam, then it is to have a high skill in the areas covered. 
  
  So in the example you give, ZYX should finish the research faster than XYZ would. 
  
  When the difference between skill becomes larger, and there's only one field missing from the more skilled team the situation changes, in that case the more skilled team will finish the job quicker. A Skill-8 team with 4 matching fields is usually faster than a Skill-6 team with 5 fields, for example.
  
  However, there are some exceptions. If you build a nuclear reactor or rocket test site those sites will add skill in nuclear/rocketry fields to any research team conducting research in those areas. 
  
  So if you are researching technology that requires:
  
  
  nuclear skill  
  nuclear skill   
  nuclear skill
  mathematics skill
  organizational skill
  
  
  A tech team with just nuclear skill will outperform a tech team with math/organizational skill if you have no nuclear reactor, but if you do have a reactor the math/organizational team will be your preferred choice. 
  
  There are several other factors which influence tech research speed like blueprints or the tech's historical year. 
  
  A great article to read trough if you want to know more about the math behind research speeds is the article on the HOI 2 wiki about research
  
  If you want to figure out who is the absolute fastest team to get a certain tech I would recommend using a tool like the research tool as all the different factors which influence research speed can make making the right choice very hard.